The ordinary ability of all intact humans to understand spoken language is not, as yet, well understood. A decade of psycholinguistic research has, however, defined a number of particular problems, the solutions of which are of particular importance to an understanding of the human Language Comprehension System (LCS). One such problem is to explain the ability of the LCS to retrieve information from the hearer's internalized lexicon. This retrieval must take place with great speed and--since we assume that speech is received in linear order--using information based on the linguistic context immediately prior to the lexical item. If this assumption is correct, then it is also true that the lexical retrieval processes must frequently culminate in a grossly under-determined decision about the meaning of the lexical item in question because most, if not all lexical items are ambiguous even in context, and most, if not all, sentences are ambiguous prior to their conclusion. The proposed experiments will investigate the activity of the LCS when it is confronted with an ambiguous lexical item in a sentential context. Previous research has shown that the LCS derives only one meaning for the lexically ambiguous sentence. The present research will test the hypothesis that one semantic reading is chosen for an ambiguous lexical item immediately after it is received by the LCS (the "early decision hypothesis"). A variety of experimental techniques will be used to test variables which operate during sentence processing. The results obtained will have implications for a number of current issues in psycholinguistic theory.